/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.calcite.rel.hint;

import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rel.core.Join;
import org.apache.calcite.rel.core.Project;
import org.apache.calcite.rel.core.TableScan;

/**
 * A hint strategy that specifies which kind of relational
 * expression the hint can be applied to.
 */
public class NodeTypeHintStrategy implements HintStrategy {

  /**
   * Enumeration of the relational expression types that the hints
   * may be propagated to.
   */
  enum NodeType {
    /**
     * The hint is used for the whole query, kind of like a query config.
     * This kind of hints would never be propagated.
     */
    SET_VAR(RelNode.class),

    /**
     * The hint would be propagated to the Join nodes.
     */
    JOIN(Join.class),

    /**
     * The hint would be propagated to the TableScan nodes.
     */
    TABLE_SCAN(TableScan.class),

    /**
     * The hint would be propagated to the Project nodes.
     */
    PROJECT(Project.class);

    /** Relational expression clazz that the hint can apply to. */
    private Class<?> relClazz;

    NodeType(Class relClazz) {
      this.relClazz = relClazz;
    }
  }

  private NodeType nodeType;

  public NodeTypeHintStrategy(NodeType nodeType) {
    this.nodeType = nodeType;
  }

  @Override public boolean supportsRel(RelHint hint, RelNode rel) {
    switch (this.nodeType) {
    // The SET_VAR type never propagate any hints.
    case SET_VAR:
      return false;
    default:
      return this.nodeType.relClazz.isInstance(rel);
    }
  }
}

// End NodeTypeHintStrategy.java
